In a transmission network, to realize traffic engineering, constrained path computation is often carried out in accordance with a bandwidth, a price, a label resource and the like. To realize such path computation, the Internet Engineering Task Force (IETF) proposes a path computation element (PCE) for processing all path computation requests in one routing domain or coordinating the PCE in a plurality of domains to process the path computation requests across the plurality of routing domains. The PCE is generally called as a path computation server, and relatively, a requester of the path computation is called as a path computation client (PCC), and the PCE is interacted with the PCC by adopting a path computation element protocol (PCEP). The PCC sends a path computation request (PCReq) to the PCE, and the PCE carries out the constrained path computation according to an own traffic engineering database (TED), and then returns a path result to the PCC through a path computation response (PCRep), thereby completing a path computation.
According to description of RFC4655, the PCE can be classified into a stateless mode and a stateful mode. The stateless PCE can be only synchronized with the TED in topology, and does not understand a state of an existing traffic engineering (TE) label switched path (LSP) in a network. However, the stateful PCE can also be synchronized with LSP DB, in addition to be synchronized with the TED, thereby grasping the state of the existing TE LSP. In this way, for the stateful PCE, information on a full life circle of the LSP is obtained, and the stateful PCE also has an LSP management capability which is an LSP management capability based on a global view, like control plane nodes. The capability can provide more flexible and effective help for the path computation and management of the PCE. The stateful PCE is also one of important characteristics of evolving to a software defined network (SDN).
An implementation framework of the stateful PCE is described in a standard draft draft-ietf-pce-stateful-pce of the IETF. A capability supported by the stateful PCE is negotiated through an Open message when a PCC end and a PCE end initialize a PCEP session. If the negotiation is succeeded, the PCC end starts to report an LSP state to the PCE when the LSP state is changed. As shown in FIG. 1, when the LSP state at a PCC side is changed, a change situation of the LSP state is continuously reported to the stateful PCE through PCRpt message. This is a general process of reporting the LSP state report.
Application scenarios of the stateful PCE are described in the draft draft-ietf-pce-stateful-pce-app-01 of the IETF. After the stateful PCE is restarted in survivability of the PCE in section 4.3, a session is established by the started PCE and each PCC in an existing mode, and once the session is successfully established, the PCC reports the LSP state report to the PCE immediately, and carries out synchronization of the LSP state.
However, the transient LSP state report may cause that the PCE is overloaded or is not processed in time. Some other methods are also proposed in the draft, for example, solution 1: with a locally stored backup, the stateful PCE can firstly recover from the backup after being started, or solution 2: synchronization is carried out from another stateful PCE on a premise of realizing host and backup of the stateful PCE. But for solution 1, a new state report and a backup need to be contrasted one by one to keep consistent subsequently in this mode, and the amount of computation is not small; and due to a real-time change of the state report, the backup also needs to be backed up in real time, thereby aggravating an I/O burden of the stateful PCE; and for solution 2, the premise is that the host and backup of the stateful PCE are realized, causing high deployment cost.
In addition, if the stateful PCE needs to be switched to the stateless PCE currently, the PCEP session of the PCE and all PCC nodes must be disconnected; and session establishment is reissued, which indicates no capability of the stateful PCE. This mode has a large influence in a current network, but cannot forbid the PCC to report the LSP state report if the session is not disconnected.